Maui County Water Samples

Author

Alemarie Ceria

Published

November 3, 2025

Get Coordinates of Water Sampling Locations

Goal

Webscrape and extract the coordinates of all points within the Department of Water Supply - Water Advisory Area Address Locator Web App.

Tracing Web App Requests to APIs

Locate Feature Service Endpoints

The legend shows that the water samples come from three spatial layers: hydrant, property, and WTP/tank. To see where the data is being pulled from, we need to find the request URLs using the Chrome DevTools (inspect element tool) by:

  1. Going to the “Network” tab
  2. Pressing the “Fetch/XHR” button to filter to requests
  3. Filtering to PBF data, which holds the feature data by inputting “query?f=pbf” into the filter bar
  4. Clicking one of the queries within the “Name” box
  5. Inspecting the Request URL to get the base URL

Here, we can see that the water sample data is being pulled from the SAMPLES feature server: https://services3.arcgis.com/fsrDo0QMPlK9CkZD/arcgis/rest/services/SAMPLES/FeatureServer/.

From there, we can see the three layers listed and their IDs. We can also go to the map viewer to confirm if this is actually the data we want to be requesting.

Build Queries

Here are the feature layer base URLs:

  1. Hydrant Water Samples: https://services3.arcgis.com/fsrDo0QMPlK9CkZD/arcgis/rest/services/SAMPLES/FeatureServer/0
  2. Property Water Samples: https://services3.arcgis.com/fsrDo0QMPlK9CkZD/arcgis/rest/services/SAMPLES/FeatureServer/1
  3. WTP/Tank Water Samples: https://services3.arcgis.com/fsrDo0QMPlK9CkZD/arcgis/rest/services/SAMPLES/FeatureServer/2

You can see the parameters you can specify in your query by:

  1. Going to the end of one of the feature layers above
  2. Clicking Query (Example URL: https://services3.arcgis.com/fsrDo0QMPlK9CkZD/ArcGIS/rest/services/SAMPLES/FeatureServer/0/query)

Data Workflow Overview

The figure below shows the automated {targets} pipeline used to download, process, and export water sample data from the Maui County Department of Water Supply ArcGIS feature service.

Summary

  1. Define layers: The feature_layers target lists the three ArcGIS feature server layers (hydrant, property, WTP/tank).
  2. Fetch counts: layer_counts queries how many records each layer contains.
  3. Download: raw_layer downloads each dataset (runs as dynamic branches in parallel).
  4. Tidy: tidied_layer cleans and standardizes each dataset’s columns and location strings.
  5. Merge: merged_ws_sf combines all tidied layers into a single spatial object (sf).
  6. Export: exported_ws_data writes the final shapefile to /data/03_output/merged_water_samples/.

Each circle in the graph represents a target (a single object or file), and each square represents dynamic branches that run independently for each layer. See R/ folder in repository for scripts used in pipeline.

Outputs

Interactive Table

Interactive Map

Hover over a point to see location name or click on it to view more details:

Next Step: Parse Results

Reproducibility

This project uses renv for dependency management.

Restore Environtment

To reproduce this environment:

renv::restore()

Session Information and Dependencies

Project directory: F:/shuler_lab_projects/voc_ws_comparison 
R version 4.5.0 (2025-04-11 ucrt)
Platform: x86_64-w64-mingw32/x64
Running under: Windows 11 x64 (build 26200)

Matrix products: default
  LAPACK version 3.12.1

locale:
[1] LC_COLLATE=English_United States.utf8 
[2] LC_CTYPE=English_United States.utf8   
[3] LC_MONETARY=English_United States.utf8
[4] LC_NUMERIC=C                          
[5] LC_TIME=English_United States.utf8    

time zone: Pacific/Honolulu
tzcode source: internal

attached base packages:
[1] stats     graphics  grDevices datasets  utils     methods   base     

other attached packages:
 [1] htmltools_0.5.8.1  fs_1.6.6           readr_2.1.5        mapview_2.11.4    
 [5] DT_0.34.0          visNetwork_2.1.4   sf_1.0-21          dplyr_1.1.4       
 [9] tarchetypes_0.13.2 targets_1.11.4    

loaded via a namespace (and not attached):
 [1] bslib_0.9.0             xfun_0.54               raster_3.6-32          
 [4] htmlwidgets_1.6.4       processx_3.8.6          lattice_0.22-6         
 [7] tzdb_0.5.0              callr_3.7.6             leaflet.providers_2.0.0
[10] vctrs_0.6.5             tools_4.5.0             crosstalk_1.2.2        
[13] ps_1.9.1                generics_0.1.4          stats4_4.5.0           
[16] base64url_1.4           parallel_4.5.0          tibble_3.3.0           
[19] proxy_0.4-27            pkgconfig_2.0.3         KernSmooth_2.23-26     
[22] satellite_1.0.6         data.table_1.17.8       secretbase_1.0.5       
[25] RColorBrewer_1.1-3      uuid_1.2-1              leaflet_2.2.3          
[28] lifecycle_1.0.4         compiler_4.5.0          farver_2.1.2           
[31] textshaping_1.0.4       terra_1.8-70            codetools_0.2-20       
[34] sass_0.4.10             class_7.3-23            yaml_2.3.10            
[37] jquerylib_0.1.4         pillar_1.11.1           classInt_0.4-11        
[40] cachem_1.1.0            brew_1.0-10             tidyselect_1.2.1       
[43] digest_0.6.37           rprojroot_2.1.1         fastmap_1.2.0          
[46] grid_4.5.0              here_1.0.2              cli_3.6.5              
[49] magrittr_2.0.4          base64enc_0.1-3         leafem_0.2.5           
[52] e1071_1.7-16            withr_3.0.2             prettyunits_1.2.0      
[55] scales_1.4.0            backports_1.5.0         sp_2.2-0               
[58] rmarkdown_2.30          igraph_2.2.1            hms_1.1.4              
[61] png_0.1-8               evaluate_1.0.5          knitr_1.50             
[64] rlang_1.1.6             leafpop_0.1.0           Rcpp_1.1.0             
[67] glue_1.8.0              DBI_1.2.3               renv_1.1.5             
[70] svglite_2.2.2           rstudioapi_0.17.1       jsonlite_2.0.0         
[73] R6_2.6.1                systemfonts_1.3.1       units_1.0-0

For the complete dependency list, see the renv.lock file.

Environment Status

No issues found -- the project is in a consistent state.